Asphalt pavements deteriorate over time due to the impact of traffic, water and sunlight. The deterioration in pavement quality can lead to permanent deformation or rutting, cracking or brittleness and can lead to inferior skid resistance. The deterioration is evident from a decrease in penetration value (for example measured at 25° C. in accordance with EN 1426 or ASTM D5-97) and an increase in softening point (for example measured using the Ring and Ball technique in accordance with EN 1427 or ASTM D36-95).
Recycling techniques offer a means of recovering desirable pavement properties without replacing the entire pavement with new materials. Additionally they enable reuse of production waste from the asphalt pavement industry. Recycling asphalt pavements has the advantages of decreasing the demand for natural resources, decreasing the production of waste material and reducing costs. Desirably the amount of the asphalt pavement that is recycled is maximised and the amount of new material that is added to the recovered asphalt is minimised.
Reclaimed asphalt pavement (known as RAP) can be recycled “in-place” (i.e. at the road location), or can be recycled “in-plant” (i.e. the RAP is removed from the road surface and transported to an asphalt mix plant). In a hot in-place recycling process, the existing pavement is reheated and milled and virgin aggregate and a rejuvenating agent are added to the RAP. This process is primarily used for resurfacing the top layer of a pavement and can re-use up to 100% of the RAP. In a hot in-plant recycling process, the RAP is broken and milled, and virgin aggregate, a rejuvenating agent and, in some instances, fresh bitumen are added. The in-plant process may be used for the construction of new base layers, but it can be difficult to incorporate a high level of RAP into the final product at the date of the invention due to constraints of the asphalt mix plant, and typically the final product consists of up to about 50% PAP.
The function of the rejuvenating agent (also known as a recycling agent) is to modify the properties of the aged binder contained in the RAP so that the recycled asphalt has properties resembling those of the original asphalt. It may not be possible to restore the asphalt to its former state, but it should be possible to significantly improve those properties that have been subject to deterioration.
A rejuvenating agent that is commonly used is a low viscosity product obtained from crude oil distillation. The present inventors have sought to provide an alternative rejuvenating agent, and have sought to provide an agent wherein at least a proportion of the agent is a natural product of plant origin. Incorporating a plant product instead of a petroleum product offers a potentially more sustainable product, and may lead to price and supply advantages. The natural-product based rejuvenating agent must have the required technical properties and in use should be safe and easy to handle.
EP 1 491 684 describes a process for the renovation of road surfacings wherein the old surface is removed, the moisture content is adjusted and a binder is added in the cold state. The binder and RAP are mixed and then rolled to form the renovated surfacing. The binder consists of at least bitumen and animal or vegetable oil. In the preferred embodiment, the binder contains 10 wt % of rapeseed oil, 60 wt % of bitumen and 30 wt % of polymer bitumen. The binder described in EP 1 491 684 has been formulated specifically for use in cold in-place recycling, a process which is primarily used to recycle the base layer of low to medium trafficked roads. By contrast, hot recycling processes can be used to rejuvenate the surface layers of roads.
In a thesis entitled “The Use of Palm Oil Products to Modify and Rejuvenate Bitumens” by Hasanan bin Md. Nor, submitted to the Faculty of Civil Engineering at the Universiti Teknologi Malaysia in 1994, the use of palm olein and palm kernel olein as rejuvenating agents is described. Palm oil is oil obtained from the flesh of the fruit of the oil palm. Palm kernel oil is oil obtained from the kernel of the oil palm fruit. Palm olein and palm kernel oleins are obtained after crystallisation of palm oil and palm kernel oil, respectively, at a controlled temperature. In the recommendations of the thesis it is recommended to use oleins with fresh bitumen or polymer-modified bitumen in processes for recycling asphalt.
The present inventors have sought to provide an alternative rejuvenating agent that comprises a plant-based product and that can be used in hot in-place and in-plant recycling processes.